The long range goal is to understand the processing of electrosensory information in electric fish of the family Mormyridae and to apply the results to general neurobiological problems. This proposal focuses on the electrosensory lobe, a cerebellum-like structure in which electroreceptor afferents of all three types (ampullary, knollenorgan, and mormyromast) terminate, each within a separate region. At the time of an electric organ discharge (EOD), each region is affected not only by the evoked afferent input but also by a corollary discharge of the EOD motor command (EOCD). The form of the EOCD matches the pattern of EOD evoked input. This matching is of two types. An invariant type in which predictable input features are matched by corresponding EOCD features and a modifiable or plastic type. The latter has as yet been seen only in the ampullary region where changes in the EOD evoked input pattern are matched by subsequent changes in the EOCD. This proposal focuses on the mormyromast region because it is the largest region, and because it is the subsystem responsible for active electrolocation. There are two objectives. The first is a physiological and anatomical study of the mormyromast region which seeks to describe the flow of information through the local circuitry. This includes an analysis of EOCD effects and testing for EOCD plasticity. Experiments will be done in curarized fish where the EOCD can be examined in isolation. Single cells and fibers will be recorded both extra- and intracellularly. The effects of electrosensory input, of EOCD's, and the interaction between these two will be examined. Cells will be injected with HRP for anatomical identification and description. Some synaptic structures will be examined with the electron microscope. The second objective of the proposed research is to determine the duration and the site of the plastic change in the EOCD which has been found in the ampullary region and which is expected in the mormyromast region. Methods will include recording, stimulation, and lesions. The general problems to which the proposed work may be relevant include: information processing in local circuits; effects of motor commands on sensory input; storage and retrieval of neural images; and cerebellar function.